The invention relates generally to the field of cytogenetics, and more particularly, to the field of molecular cytogenetics. The invention concerns methods for identifying and classifying chromosomes. Still more particularly, this invention concerns nucleic acid probes which can be designed by the processes described herein to produce staining distributions that can extend along one or more whole chromosomes, and/or along a region or regions on one or more chromosomes, including staining patterns that extend over the whole genome. Staining patterns can be tailored for any desired cytogenetic application, including prenatal, tumor and disease related cytogenetic applications, among others. The invention provides for compositions of nucleic acid probes and for methods of staining chromosomes therewith to identify normal chromosomes and chromosomal abnormalities in metaphase spreads and in interphase nuclei. The probe-produced staining patterns of this invention facilitate the microscopic and/or flow cytometric identification of normal and abnormal chromosomes and the characterization of the genetic nature of particular abnormalities. The particular focus of this application is that wherein the abnormalities are genetic rearrangements.
Although most of the examples herein concern human chromosomes and much of the language herein is directed to human concerns, the concept of using nucleic acid probes for staining or painting chromosomes is applicable to chromosomes from any source including both plants and animals.
Chromosome abnormalities are associated with genetic disorders, degenerative diseases, and exposure to agents known to cause degenerative diseases, particularly cancer, German, xe2x80x9cStudying Human Chromosomes Today,xe2x80x9d American Scientist Vol. 58, pgs. 182-201 (1970); Yunis, xe2x80x9cThe Chromosomal Basis of Human Neoplasia,xe2x80x9d Science Vol. 221, pgs. 227-236 (1983); and German, xe2x80x9cClinical Implication of Chromosome Breakage,xe2x80x9d in Genetic Damage in Man Caused by Environmental Agents, Berg, Ed., pgs. 65-86 (Academic Press, New York, 1979). Chromosomal abnormalities can be of several types, including: extra or missing individual chromosomes, extra or missing portions of a chromosome (segmental duplications or deletions), breaks, rings and chromosomal rearrangements, among others. Chromosomal or genetic rearrangements include translocations (transfer of a piece from one chromosome onto another chromosome), dicentrics (chromosomes with two centromeres), inversions (reversal in polarity of a chromosomal segment), insertions, amplifications, and deletions.
Detectable chromosomal abnormalities occur with a frequency of one in every 250 human births. Abnormalities that involve deletions or additions of chromosomal material alter the gene balance of an organism and generally lead to fetal death or to serious mental and physical defects. Down syndrome can be caused by having three copies of chromosome 21 instead of the normal 2. This syndrome is an example of a condition caused by abnormal chromosome number, or aneuploidy. Down syndrome can also be caused by a segmental duplication of a subregion on chromosome 21 (such as, 21q22), which can be present on chromosome 21 or on another chromosome. Edward syndrome (18+), Patau syndrome (13+), Turner syndrome (XO) and Kleinfelter syndrome (XXY) are among the most common numerical aberrations. [Epstein, The Consequences of Chromosome Imbalance: Principles, Mechanisms and Models (Cambridge Univ. Press 1986); Jacobs, Am. J. Epidemiol, 105:180 (1977); and Lubs et al., Science, 169:495 (1970).]
Retinoblastoma (del 13q14), Prader-Willi syndrome (del 15q11-q13), Wilm""s tumor (del 11p13) and Cri-du-chat syndrome (del 5p) are examples of important disease linked structural aberrations. [Nora and Fraser, Medical Genetics: Principles and Practice. (Lea and Febiger 1989).]
Measures of the frequency of structurally aberrant chromosomes, for example, dicentric chromosomes, caused by clastogenic agents, such as, ionizing radiation or chemical mutagens, are widely used as quantitative indicators of genetic damage caused by such agents, Biochemical Indicators of Radiation Injury in Man (International Atomic Energy Agency, Vienna, 1971); and Berg, Ed. Genetic Damage in Man Caused by Environmental Agents (Academic Press, New York, 1979). A host of potentially carcinogenic and teratogenic chemicals are widely distributed in the environment because of industrial and agricultural activity. These chemicals include pesticides, and a range of industrial wastes and by-products, such as halogenated hydrocarbons, vinyl chloride, benzene, arsenic, and the like, Kraybill et al., Eds., Environmental Cancer (Hemisphere Publishing Corporation, New York, 1977). Sensitive measures of chromosomal breaks and other abnormalities could form the basis of improved dosimetric and risk assessment methodologies for evaluating the consequences of exposure to such occupational and environmental agents.
Current procedures for genetic screening and biological dosimetry involve the analysis of karyotypes. A karyotype is the particular chromosome complement of an individual or of a related group of individuals, as defined both by the number and morphology of the chromosomes usually in mitotic metaphase. It includes such things as total chromosome number, copy number of individual chromosome types (e.g., the number of copies of chromosome X), and chromosomal morphology, e.g., as measured by length, centromeric index, connectedness, or the like. Chromosomal abnormalities can be detected by examination of karyotypes. Karyotypes are conventionally determined by staining an organism""s metaphase, or otherwise condensed (for example, by premature chromosome condensation) chromosomes. Condensed chromosomes are used because, until recently, it has not been possible to visualize interphase chromosomes due to their dispersed condition and the lack of visible boundaries between them in the cell nucleus.
A number of cytological techniques based upon chemical stains have been developed which produce longitudinal patterns on condensed chromosomes, generally referred to as bands. The banding pattern of each chromosome within an organism usually permits unambiguous identification of each chromosome type, Latt, xe2x80x9cOptical Studies of Metaphase Chromosome Organization,xe2x80x9d Annual Review of Biophysics and Bioengineering, Vol. 5, pgs. 1-37 (1976). Accurate detection of some important chromosomal abnormalities, such as translocations and inversions, has required such banding analysis.
Unfortunately, such conventional banding analysis requires cell culturing and preparation of high quality metaphase spreads, which is time consuming and labor intensive, and frequently difficult or impossible. For example, cells from many tumor types are difficult to culture, and it is not clear that the cultured cells are representative of the original tumor cell population. Fetal cells capable of being cultured need to be obtained by invasive means and need to be cultured for several weeks to obtain enough metaphase cells for analysis. In many cases, the banding patterns on the abnormal chromosomes do not permit unambiguous identification of the portions of the normal chromosomes that make them up. Such identification may be important to indicate the location of important genes involved in the abnormality. Further, the sensitivity and resolving power of current methods of karyotyping are limited by the fact that multiple chromosomes or chromosomal regions have highly similar staining characteristics, and that abnormalities (such as deletions) which involve only a fraction of a band are not detectable. Therefore, such methods are substantially limited for the diagnosis and detailed analysis of contiguous gene syndromes, such as partial trisomy, Prader-Willi syndrome [Emanuel, Am. J. Hum. Genet. 43:575 (1988); Schmickel, J. Pediatr., 109:231 (1986)] and retinoblastoma [Sparkes, Biochem. Biophys. Acta., 780:95 (1985)].
Thus, conventional banding analysis has several important limitations, which include the following. 1) It is labor intensive, time consuming, and requires a highly trained analyst. 2) It can be applied only to condensed chromosomes. 3) It does not allow for the detection of structural aberrations involving less than 3-15 megabases (Mb), depending upon the nature of the aberration and the resolution of the banding technique [Landegren et al., Science 242:229 (1988)]. This invention provides for probe compositions and methods to overcome such limitations of conventional banding analysis.
The chemical staining procedures of the prior art provide patterns over a genome for reasons not well understood and which cannot be modified as required for use in different applications. Such chemical staining patterns were used to map the binding site of probes. However, only occasionally, and with great effort, was in situ hybridization used to obtain some information about the position of a lesion, for example, a breakpoint relative to a particular DNA sequence. The present invention overcomes the inflexibility of chemical staining in that it stains a genome in a pattern based upon nucleic acid sequence; therefore the pattern can be altered as required by changing the nucleic acid sequence of the probe. The probe-produced staining patterns of this invention provide reliable fundamental landmarks which are useful in cytogenetic analysis.
Automated detection of structural abnormalities of chromosomes with image analysis of chemically stained bands would require the development of a system that can detect and interpret the banding patterns produced on metaphase chromosomes by conventional techniques. It has proven to be very difficult to identify reliably by automated means normal chromosomes that have been chemically stained; it is much more difficult to differentiate abnormal chromosomes having structural abnormalities, such as, translocations. Effective automated detection of translocations in conventionally banded chromosomes has not been accomplished after over a decade of intensive work. The probe-produced banding patterns of this invention are suitable for such automated detection and analysis.
In recent years rapid advances have taken place in the study of chromosome structure and its relation to genetic content and DNA composition. In part, the progress has come in the form of improved methods of gene mapping based on the availability of large quantities of pure DNA and RNA fragments for probes produced by genetic engineering techniques, e.g., Kao, xe2x80x9cSomatic Cell Genetics and Gene Mapping,xe2x80x9d International Review of Cytology Vol. 85, pgs. 109-146 (1983), and D""Eustachio et al., xe2x80x9cSomatic Cell Genetics in Gene Families,xe2x80x9d Science, Vol. 220, pgs. 9, 19-924 (1983). The probes for gene mapping comprise labeled fragments of single-stranded or double-stranded DNA or RNA which are hybridized to complementary sites on chromosomal DNA. With such probes it has been crucially important to produce pure, or homogeneous, probes to minimize hybridizations at locations other than at the site of interest, Henderson, xe2x80x9cCytological Hybridization to Mammalian Chromosomes,xe2x80x9d International Review of Cytology Vol. 76, pgs. 1-46 (1982).
The hybridization process involves unravelling, or melting, the double-stranded nudeic acids of the probe and target by heating, or other means (unless the probe and target are single-stranded nucleic acids). This step is sometimes referred to as denaturing the nudeic acid. When the mixture of probe and target nucleic acids cool, strands having complementary bases recombine, or anneal. When a probe anneals with a target nudeic acid, the probe""s location on the target can be detected by a label carried by the probe or by some intrinsic characteristics of the probe or probe-target duplex. When the target nucleic acid remains in its natural biological setting, e.g., DNA in chromosomes, mRNA in cytoplasm, portions of chromosomes or cell nuclei (albeit fixed or altered by preparative techniques), the hybridization process is referred to as in situ hybridization.
In situ hybridization probes were initially limited to identifying the location of genes or other well defined nucleic acid sequences on chromosomes or in cells. Comparisons of the mapping of single-copy probes to normal and abnormal chromosomes were used to examine chromosomal abnormalities. Cannizzaro et al., Cytogenetics and Cell Genetics, 39:173-178 (1985). Distribution of the multiple binding sites of repetitive probes could also be determined.
Hybridization with probes which have one target site in a haploid genome, single-copy or unique sequence probes, has been used to map the locations of particular genes in the genome [Harper and Saunders, xe2x80x9cLocalization of the Human Insulin Gene to the Distal End of the Short Arm of Chromosome 11,xe2x80x9d Proc. Natl. Acad. Sci., Vol. 78, pgs. 4458-4460 (1981); Kao et al., xe2x80x9cAssignment of the Structural Gene Coding for Albumin to Chromosome 4,xe2x80x9d Human Genetics, Vol. 62, pgs. 337-341 (1982)]; but such hybridizations are not reliable when the size of the target site is small. As the amount of target sequence for low complexity single-copy probes is small, only a portion of the potential target sites in a population of cells form hybrids with the probe. Therefore, mapping the location of the specific binding site of the probe has been complicated by background signals produced by non-specific binding of the probe and also by noise in the detection system (for example, autoradiography or immunochemistry). The unreliability of signals for such prior art single-copy probes has required statistical analysis of the positions of apparent hybridization signals in multiple cells to map the specific binding site of the probe.
Wallace et al., in xe2x80x9cThe Use of Synthetic Oligonucleotides as Hybridization Probes. II. Hybridization of Oligonudeotides of Mixed Sequence to Rabbit Beta-Globin DNA,xe2x80x9d Nucleic Acids Research, Vol. 9, pgs. 879-894 (1981), disclose the construction of synthetic oligonucleotide probes having mixed base sequences for detecting a single locus corresponding to a structural gene. The mixture of base sequences was determined by considering all possible nucleotide sequences which could code for a selected sequence of amino acids in the protein to which the structural gene corresponded.
Olsen et al., in xe2x80x9cIsolation of Unique Sequence Human X Chromosomal Deoxyribonucleic Acid,xe2x80x9d Biochemistry, Vol. 19, pgs. 2419-2428 (1980), disclose a method for isolating labeled unique sequence human X chromosomal DNA by successive hybridizations: first, total genomic human DNA against itself so that a unique sequence DNA fraction can be isolated; second, the isolated unique sequence human DNA fraction against mouse DNA so that homologous mouse/human sequences are removed; and finally, the unique sequence human DNA not homologous to mouse against the total genomic DNA of a human/mouse hybrid whose only human chromosome is chromosome X, so that a fraction of unique sequence X chromosomal DNA is isolated. Individual clones are then isolated from this fraction and are candidates for human X chromosome specific DNA sequences.
Manuelidis et al., in xe2x80x9cChromosomal and Nuclear Distribution of the Hind III 1.9-KB Human DNA Repeat Segment,xe2x80x9d Chromosoma Vol. 91, pp. 28-38 (1984), disclose the construction of a single kind of DNA probe for detecting multiple loci on chromosomes corresponding to the location of members of a family of repeated DNA sequences. Such probes are herein termed repetitive probes.
Different repetitive sequences may have different distributions on chromosomes. They may be spread over all chromosomes as in the just cited reference, or they may be concentrated in compact regions of the genome, such as, on the centromeres of the chromosomes, or they may have other distributions. In some cases, such a repetitive sequence is predominantly located on a single chromosome, and therefore is a chromosome-specific repetitive sequence. [Willard et al., xe2x80x9cIsolation and Characterization of a Major Tandem Repeat Family from the Human X Chromosome,xe2x80x9d Nucleic Acids Research, Vol. 11, pgs. 2017-2033 (1983).]
A probe for repetitive sequences shared by all chromosomes can be used to discriminate between chromosomes of different species if the sequence is specific to one of the species. Total genomic DNA from one species which is rich in such repetitive sequences can be used in this manner. [Pinkel et al. (III), PNAS USA, 83:2934 (1986); Manuelidis, Hum. Genet., 71:288 (1985) and Durnam et al., Somatic Cell Molec. Genet., 11:571 (1985.]
Recently, there has been an increased availability of probes for repeated sequences (repetitive probes) that hybridize intensely and specifically to selected chromosomes. [Trask et al., Hum. Genet., 78:251 (1988) and references cited therein.] Such probes are now available for over half of the human chromosomes. In general, they bind to repeated sequences on compact regions of the target chromosome near the centromere. However, one probe has been reported that hybridizes to human chromosome 1p36, and there are several probes that hybridize to human chromosome Yq. Hybridization with such probes permits rapid identification of chromosomes in metaphase spreads, determination of the number of copies of selected chromosomes in interphase nuclei [Pinkel et al. (I), PNAS USA, 83:2934 (1986); Pinkel et al. (II), Cold Spring Harbor Symp. Quant. Biol., 51:151 (1986) and Cremer et al., Hum. Genet, 74:346 (1986)] and determination of the relative positions of chromosomes in interphase nuclei [Trask et al., supra; Pinkel et al. (I), supra; Pinkel et al. (II), supra; Manuelidis, PNAS USA, 81:3123 (1984); Rappold et al., Hum. Genet., 67:317 (1984); Schardin et al., Hum. Genet., 71:282 (1985); and Manuelidis, Hum. Genet., 71:288 (1985)].
However, many applications are still limited by the lack of appropriate probes. For example, until the methods described herein were invented, probes with sufficient specificity for prenatal diagnosis were not available for chromosome 13 or 21. Further, repetitive probes are not very useful for detection of structural aberrations since the probability is low that the aberrations will involve the region to which the probe hybridizes.
This invention overcomes the prior art limitations on the use of probes and dramatically enhances the application of in situ hybridization for cytogenetic analysis. As indicated above, prior art probes have not been useful for in-depth cytogenetic analysis. Low complexity single-copy probes do not at this stage of hybridization technology generate reliable signals. Although repetitive probes do provide reliable signals, such signals cannot be tailored for different applications because of the fixed distribution of repetitive sequences in a genome. The probes of this invention combine the hybridization reliability of repetitive probes with the flexibility of being able to tailor the binding pattern of the probe to any desired application.
The enhanced capabilities of the probes of this invention come from their increased complexity. Increasing the complexity of a probe increases the probability, and therefore the intensity, of hybridization to the target region, but also increases the probability of non-specific hybridizations resulting in background signals. However, within the concept of this invention, it was considered that such background signals would be distributed approximately randomly over the genome. Therefore, the net result is that the target region could be visualized with increased contrast against such background signals.
Exemplified herein are probes in an approximate complexity range of from about 50,000 bases (50 kb) to hundreds of millions of bases. Such representative probes are for compact loci and whole human chromosomes. Prior to this invention, probes employed for in situ hybridization techniques had complexities below 40 kb, and more typically on the order of a few kb.
Staining chromosomal material with the probes of this invention is significantly different from the chemical staining of the prior art. The specificity of the probe produced staining of this invention arises from an entirely new sourcexe2x80x94the nucleic acid sequences in a genome. Thus, staining patterns of this invention can be designed to highlight fundamental genetic information important to particular applications.
The procedures of this invention to construct probes of any desired specificity provide significant advances in a broad spectrum of cytogenetic studies. The analysis can be carried out on metaphase chromosomes and interphase nuclei. The techniques of this invention can be especially advantageous for applications where high-quality banding by conventional methods is difficult or suspected of yielding biased information, e.g., in tumor cytogenetics. Reagents targeted to sites of lesions known to be diagnostically or prognostically important, such as tumor type-specific translocations and deletions, among other tumor specific genetic arrangements, permit rapid recognition of such abnormalities. Where speed of analysis is the predominant concern, e.g., detection of low-frequency chromosomal aberrations induced by toxic environmental agents, the compositions of this invention permit a dramatic increase in detection efficiency in comparison to previous techniques based on conventional chromosome banding.
Further, prenatal screening for disease-linked chromosome aberrations (e.g., trisomy 21) is enhanced by the rapid detection of such aberrations by the methods and compositions of this invention. Interphase aneuploidy analysis according to this invention is particularly significant for prenatal diagnosis in that it yields more rapid results than are available by cell culture methods. Further, fetal cells separated from maternal blood, which cannot be cultured by routine procedures and therefore cannot be analysed by conventional karyotyping techniques, can be examined by the methods and compositions of this invention. In addition, the intensity, contrast and color combinations of the staining patterns, coupled with the ability to tailor the patterns for particular applications, enhance the opportunities for automated cytogenetic analysis, for example, by flow cytometry or computerized microscopy and image analysis.
This application specifically claims chromosome specific reagents for the detection of genetic rearrangements and methods of using such reagents to detect such rearrangements. Representative genetic rearrangements so detected are those that produce a fusion genexe2x80x94BCR-ABLxe2x80x94that is diagnostic for chronic myelogenous leukemia (CML) and those associated with chromosomes 3, 13 (retinoblastoma gene therein), and 17, such as, deletions, amplifications and translocations thereof.
Chronic myelogenous leukemia (CML) is a neoplastic proliferation of bone marrow cells genetically characterized by the fusion of the BCR and ABL genes on chromosomes 9 and 22. That fusion usually involves a reciprocal translocation t(9;22)(q34;q11), which produces the cytogenetically distinctive Philadelphia chromosome (Ph1). However, more complex rearrangements may cause BCR-ABL fusion. At the molecular level, fusion can be detected by Southern analysis or by in vitro amplification of the mRNA from the fusion gene using the polymerase chain reaction (PCR). Those techniques are sensitive but cannot be applied to single cells.
Clearly, a sensitive method for detecting chromosomal abnormalities and, more specifically, genetic rearrangements, such as, for example, the tumor specific arrangements associated with CML, the chromosome 3 and 17 deletions, amplifications and translocations associated with various cancers, and those associated with the retinoblastoma gene, would be a highly useful tool for genetic screening. This invention provides such tools.
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Fusion of the proto-oncogene c-ABL from the long arm of chromosome 9 with the BCR gene of chromosome 22 is a consistent finding in CML (1-3). That genetic change leads to formation of a BCR-ABL transcript that is translated to form a 210 kd protein present in virtually all cases of CML (46). In 90% of the cases, the fusion gene results from a reciprocal translocation involving chromosomes 9 and 22 producing a cytogenetically distinct small acrocentric chromosome called the Philadelphia (Ph1) chromosome (7-12), FIG. 8. However, standard cytogenetics does not have the resolution to distinguish closely spaced breakpoints, such as those characteristic of CML and acute lymphocytic leukemia (ALL), and misses fusions produced by more complex rearrangements. Mapping and cloning of the breakpoint regions in both genes has lead to molecular techniques capable of demonstrating BCR-ABL fusion in CML cases where the Ph1 chromosome could not be detected cytogenetically (13-16). Southern analysis for BCR rearrangements has become the standard for diagnosis of CML. More recently, fusion has been detected by in vitro amplification of a cDNA transcript copied from CML mRNA using reverse transcriptase (17-23). That technique permits detection of BCR-ABL transcript from CML cells present at low frequencies. Both of those techniques utilize nucleic acid obtained from cell populations so that correlation between genotype and phenotype for individual cells is not possible.
Chromosomal deletions involving tumor suppressor genes may play an important role in the development and progression of solid tumors. The retinoblastoma gene (Rb-1), located in chromosome 13q14, is the most extensively characterized tumor suppressor gene (Friend et al., 1986; Lee et al., 1987; Fung et al., 1987). The Rb-1 gene product, a 105 kDa nuclear phosphoprotein, apparently plays an important role in cell cycle regulation (Lee et al., 1987; Howe et al., 1990). Altered or lost expression of the Rb protein is caused by inactivation of both gene alleles either through a point mutation or a chromosomal deletion. Rb-1 gene alterations have been found not only in retinoblastomas (Friend et al., 1986; Lee et al., 1987; Fung et al., 1987) but also in other malignancies such as osteosarcomas (Friend et al. 1986), small cell lung cancer (Hensel et al., 1990; Rygaard et al., 1990) and breast cancer (Lee et al., 1988; T""Ang et al., 1988; Varley et al., 1989). Restriction fragment length polymorphism (RFLP) studies have indicated that such tumor types have frequently lost heterozygosity at 13q suggesting that one of the Rb-1 gene alleles has been lost due to a gross chromosomal deletion (Lundberg et al., 1987; Bowcock et al., 1990).
Section IX infra describes the use of fourteen lambda phage clones spanning all the exons of the Rb-1 gene region, about 150 kb of genomic DNA, as a high complexity probe for chromosome-specific painting. An intense signal produced in metaphase chromosomes confirmed the location of the Rb-1 gene at chromosome 13q14. Two Rb-1 hybridization signals were detected in about 90% of normal interphase nuclei, whereas two cell lines having a cytogenetically defined deletion involving the Rb-1 gene region showed only one hybridization signal. Gene deletion was confirmed by analyzing metaphase spreads from these cell lines cohybridized with chromosome 13/21 alpha satellite probe. Also analyzed were touch preparations and fine needle aspirates of breast carcinomas; heterogeneity was shown in Rb-1 gene copy number both within and between tumors.
Genetic rearrangements involving only subregions of the Rb-1 gene have been described (Bookstein et al., 1988; Canning and Dryja, 1989). The inventors hereof, to detect such subregions of the Rb-1 gene, used smaller probes comprising 1-5 contiguous lambda phage clones to stain specific subregions within the Rb-1 gene thus allowing detection of aberrations within that tumor suppressor gene. Such representative examples of the chromosome-specific staining methods of this invention provide information on actual gene copy numbers and rearrangements from individual morphologically defined tumor cells useful in the evaluation of neoplasia-associated gene aberrations as well as intratumor genetic heterogeneity.
The deletion of the short arm of chromosome 3 has been associated with several cancers, for example, small cell lung cancer, renal and ovarian cancers; it has been postulated that one or more putative tumor suppressor genes is or are located in the p region of chromosome 3 (ch. 3p) [Minna et al., Symposia on Quantitative Biology, Vol. L1:843-853 (CSH Lab 1986); Cohen et al., N. Eng. J. Med., 301:592-595 (1979); Bergerham et al., Cancer Res., 49:1390-1396 (1989); Whang-Peng et al., Can. Genet. Cytogenet, 11:91-106 (1984); and Trent et al., Can. Genet. Cytogenet, 14:153-161 (1985)]. As shown in Section X infra chromosome-specific staining according to this invention can be used to create bands of stained nucleic acid that detect structural aberrations, for example, those of chromosome 3. The examples of Section X demonstrate the initial stages of a probe-based banding pattern to detect genetic rearrangements of chromosome 3.
Described herein are chromosome-specific reagents and methods to detect genetic rearrangements, such as those exemplified herein for the BCR-ABL fusion, deletions, amplifications, and translocations of chromosomes 3, 17 and 13, that supply information unavailable by existing techniques.
This invention concerns methods of staining chromosomal material based upon nucleic acid sequence that employ one or more nucleic acid probes. Said methods produce staining patterns that can be tailored for specific cytogenetic analyses. It is further an object of this invention to produce nucleic acid probes that are useful for cytogenetic analysis, that stain chromosomal material with reliable signals. Such probes are appropriate for in situ hybridization. Preferred nucleic acid probes for certain applications of this invention are those of sufficient complexity to stain reliably each of two or more target sites.
The invention provides methods and compositions for staining chromosomal material. The probe compositions of this invention at the current state of hybridization techniques are typically of high complexity, usually greater than about 50 kb of complexity, the complexity depending upon the application for which the probe is designed. In particular, chromosome specific staining reagents are provided which comprise heterogeneous mixtures of nucleic acid fragments, each fragment having a substantial fraction of its sequences substantially complementary to a portion of the nucleic acid for which specific staining is desiredxe2x80x94the target nucleic acid, preferably the target chromosomal material. In general, the nucleic acid fragments are labeled by means as exemplified herein and indicated infra. However, the nucleic acid fragments need not be directly labeled in order for the binding of probe fragments to the target to be detected; for example, such nudeic acid binding can be detected by anti-RNA/DNA duplex antibodies and antibodies to thymidine dimers. The nucleic acid fragments of the heterogenous mixtures include double-stranded or single-stranded RNA or DNA.
This invention concerns chromosome specific reagents and methods of staining targeted chromosomal material that is in the vicinity of a suspected genetic earrangement. Such genetic rearrangement include but are not limited to translocations, inversions, insertions, amplifications and deletions. Aneuploidy is included herein in the term xe2x80x9camplificationsxe2x80x9d. When such a genetic rearrangement is associated with a disease, such chromosome specific reagents are referred to as disease specific reagents or probes. When such a genetic rearrangement is associated with cancer, such reagents are referred to as tumor specific reagents or probes.
This invention provides for nucleic acid probes that reliably stain targeted chromosomal materials in the vicinity of one or more suspected genetic rearrangements. Such nucleic acid probes useful for the detection of genetic rearrangements are typically of high complexity. Such nucleic acid probes preferably comprise nucleic acid sequences that are substantially homologous to nudeic acid sequences in chromosomal regions that flank and/or extend partially or fully across breakpoints associated with genetic rearrangements.
This invention further provides for methods and reagents to distinguish between cytogenetically similar but genetically different chromosomal rearrangements.
Specifically herein exemplified are chromosome specific regents and methods to detect genetic rearrangements, e.g., translocations, amplifications and insertions, that produce the BCR-ABL fusion which is diagnostic for chronic myelogenous leukemia (CML). Such chromosome specific reagents for the diagnosis of CML contain nucleic acid sequences which are substantially homologous to chromosomal sequences in the vicinity of the translocation breakpoint regions of chromosomal regions 9q34 and 22q11 associated with CML.
Those reagents produce a staining pattern which is distinctively altered when the BCR-ABL fusion characteristic of CML occurs. FIG. 11 graphically demonstrates a variety of staining patterns which, along with other potential staining patterns, are altered in the presence of a genetic rearrangement, such as, the BCR-ABL fusion.
The presence of a genetic rearrangement can be determined by applying the reagents of this invention according to methods herein described and observing the proximity of and/or other characteristics of the signals of the staining patterns produced.
Preferably, the chromosome specific reagents used to detect CML of this invention comprise nudeic acid sequences having a complexity of from about 50 kilobases (kb) to about 1 megabase (Mb), more preferably from about 50 kb to about 750 kb, and still more preferably from about 200 kb to about 400 kb.
This invention further provides for methods of distinguishing between suspected genetic rearrangements that occur in relatively close proximity in a genome wherein the chromosome specific reagents comprise nucleic acid sequences substantially homologous to nudeic acid sequences in the vicinity of said suspected genetic rearrangements. An example of such a differentiation between two potential genetic rearrangements is the differential diagnosis of CML from acute lymphocytic leukemeia (ALL).
This invention still further provides methods and reagents for producing staining patterns in a patient who is afflicted with a disease associated genetic rearrangement, such as those associated with the BCR-ABL fusion in CML, wherein said staining patterns are predictive and/or indicative of the response of a patient to various therapeutic regimens, such as chemotherapy, radiation, surgery, and transplantation, such as bone marrow transplantation. Such staining patterns can be useful in monitoring the status of such a patient, preferably on a cell by cell basis, and can be predictive of a disease recurrence for a patient that is in remission. Computer assisted microscopic analysis can assist in the interpretation of staining patterns of this invention, and the invention provides for methods wherein computer assisted microscopic analysis is used in testing patient cells on a call by cell basis, for e.g., to search for residual disease in a patient.
Still further, this invention provides for methods and reagents to determine the molecular basis of genetic disease, and to detect specific genetically based diseases.
Still further, this invention provides for methods and reagents for detecting contiguous gene syndromes comprising the in situ hybridization of nucleic acid probes which comprise sequences which are substantially homologous to nudeic acid sequences characteristic of one or more components of a contiguous gene syndrome. Representative of such a contiguous gene syndrome is Down syndrome.
Also provided are methods of simultaneously detecting genetic rearrangements of multiple loci in a genome comprising in situ hybridization of high complexity nucleic acid probes comprising nucleic acid sequences that are substantially homologous to nucleic acid sequences in multiple loci in a genome.
Still further provided are methods of searching for genetic rearrangements in a genome. For example, conventional banding analysis may indicate an abnormality in a chromosomal region of a genome under examination. Methods of this invention may include the application of nucleic acid probes, produced from the vicinity of that chromosomal region of a normal genome, by in situ hybridization to cells containing the abnormality to detail the exact location and kind of genetic rearrangement of said abnormality by observation of the staining patterns so produced.
The invention still further provides for high complexity nucleic acid probes which have been optimized for rapid, efficient and automated detection of genetic rearrangements.
One way to produce a probe of high complexity is to pool several or many clones, for example, phage, plasmid, cosmid, and/or YAC clones, among others, wherein each clone contains an insert that is capable of hybridizing to some part of the target in a genome. Another way to produce such a probe is to use the polymerase chain reaction (PCR).
Heterogeneous in reference to the mixture of labeled nucleic acid fragments means that the staining reagents comprise many copies each of fragments having different sequences and/or sizes (e.g., from the different DNA clones pooled to make the probe). In preparation for use, these fragments may be cut, randomly or specifically, to adjust the size distribution of the pieces of nucleic acid participating in the hybridization reaction.
As discussed more fully below, preferably the heterogeneous probe mixtures are substantially free from nucleic acid sequences with hybridization capacity to non-target nucleic acid. Most of such sequences bind to repetitive sequences which are shared by the target and non-target nucleic acids, that is, shared repetitive sequences.
Methods to remove undesirable nucleic acid sequences and/or to disable the hybridization capacity of such sequences are discussed more fully below. [See Section II]. Such methods include but are not limited to the selective removal or screening of shared repetitive sequences from the probe; careful selection of nucleic acid sequences for inclusion in the probe; blocking shared repetitive sequences by the addition of unlabeled genomic DNA, or, more carefully selecting nucleic acid sequences for inclusion in the blocking mixture; incubating the probe mixture for sufficient time for reassociation of high copy repetitive sequences, or the like.
Preferably, the staining reagents of the invention are applied to interphase or metaphase chromosomal DNA by in situ hybridization, and the chromosomes are identified or classified, i.e., karyotyped, by detecting the presence of the label, such as biotin or 3H, on the nucleic acid fragments comprising the staining reagent.
The invention includes chromosome staining reagents for the total genomic complement of chromosomes, staining reagents specific to single chromosomes, staining reagents specific to subsets of chromosomes, and staining reagents specific to subregions within single or multiple chromosomes. The term xe2x80x9cchromosome-specific,xe2x80x9d is understood to encompass all of these embodiments of the staining reagents of the invention. The term is also understood to encompass staining reagents made from and directed against both normal and abnormal chromosome types.
A preferred method of making the chromosome-specific staining reagents of the invention includes: 1) isolating chromosomal DNA from a particular chromosome type or target region or regions in the genome, 2) amplifying the isolated DNA to form a heterogeneous mixture of nucleic acid fragments, 3) disabling the hybridization capacity of or removing shared repeated sequences in the nucleic acid fragments, and 4) labeling the nucleic acid fragments to form a heterogeneous mixture of labeled nucleic acid fragments. As described more fully below, the ordering of the steps for particular embodiments varies according to the particular means adopted for carrying out the steps.
The present invention addresses problems associated with karyotyping chromosomes, especially for diagnostic and dosimetric applications. In particular, the invention overcomes problems which arise because of the lack of stains that are sufficiently chromosome-specific by providing reagents comprising heterogeneous mixtures of nudeic acid fragments that can be hybridized to the target DNA and/or RNA, e.g., the target chromosomes, target subsets of chromosomes, or target regions of specific chromosomes. The staining technique of the invention opens up the possibility of rapid and highly sensitive detection of chromosomal abnormalities, particularly genetic rearrangements, in both metaphase and interphase cells using standard clinical and laboratory equipment and improved analysis using automated techniques. It has direct application in genetic screening, cancer diagnosis, and biological dosimetry.
This invention further specifically provides for methods and nucleic acid probes for staining fetal chromosomal material, whether condensed, as in metaphase, or dispersed as in interphase. Still further, the invention provides for a non-embryo-invasive method of karyotyping the chromosomal material of fetal cells, wherein the fetal cells have been separated from maternal blood. Such fetal cells are preferably leukocytes and/or cytotrophoblasts. Exemplary nudeic acid probes are high complexity probes chromosome-specific for chromosome types 13, 18 and/or 21. Representative probes comprise chromosome-specific Bluescribe plasmid libraries from which a sufficient number of shared repetitive sequences have been removed or the hybridization capacity thereof has been disabled prior to and/or during hybridization with the target fetal chromosomes.
This invention still further provides for test kits comprising appropriate nucleic acid probes for use in tumor cytogenetics, in the detection of disease related loci, in the analysis of structural abnormalities, for example translocations, among other genetic rearrangements, and for biological dosimetry.
This invention further provides for prenatal screening kits comprising appropriate nudeic acid probes of this invention. This invention also provides for test kits comprising high complexity probes for the detection of genetic rearrangements, and specifically for those producing the BCR-ABL fusion characteristic of CML.
The methods and compositions of this invention permit staining of chromosomal material with patterns appropriate for a desired application. The pattern may extend over some regions of one or more chromosomes, or over some or all the chromosomes of a genome and may comprise multiple distinguishable sections, distinguishable, for example, by multiple colors. Alternatively, the pattern may be focused on a particular portion or portions of a genome, such as a portion or portions potentially containing a deletion or breakpoint that is diagnostically or prognostically important for one or more tumors, or on those portions of chromosomes having significance for prenatal diagnosis.
The staining patterns may be adjusted for the analysis method employed, for example, either a human observer or automated equipment, such as, flow cytometers or computer assisted microscopy. The patterns may be chosen to be appropriate for analysis of condensed chromosomes or dispersed chromosomal material.
It is further an object of the instant invention to detect small specific deletions invisible by conventional banding analyses, including subregion deletions within a gene, for example, the Rb-1 gene.
It is still further an object of this invention to provide methods of studying the genetic heterogeneity of cancers, such as, solid tumors, and of gene copy numbers and structural abnormalities from morphologically defined individual tumor cells.
The invention further provides for automated means of detecting and analyzing chromosomal abnormalities, particularly genetic rearrangements, as indicated by the staining patterns produced according to this invention.